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Unitrode

UC2845A Datasheet Preview

UC2845A Datasheet

Current Mode PWM Controller

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Current Mode PWM Controller
application
INFO
available
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
FEATURES
Optimized for Off-line and DC to DC
Converters
Low Start Up Current (<0.5mA)
Trimmed Oscillator Discharge Current
Automatic Feed Forward Compensation
Pulse-by-Pulse Current Limiting
Enhanced Load Response Characteristics
DESCRIPTION
The UC1842A/3A/4A/5A family of control ICs is a pin for pin compati-
ble improved version of the UC3842/3/4/5 family. Providing the nec-
essary features to control current mode switched mode power
supplies, this family has the following improved features. Start up cur-
rent is guaranteed to be less than 0.5mA. Oscillator discharge is
trimmed to 8.3mA. During under voltage lockout, the output stage
can sink at least 10mA at less than 1.2V for VCC over 5V.
The difference between members of this family are shown in the table
below.
Under-Voltage Lockout With Hysteresis
Double Pulse Suppression
High Current Totem Pole Output
Internally Trimmed Bandgap Reference
500kHz Operation
Low RO Error Amp
Part #
UC1842A
UC1843A
UC1844A
UC1845A
UVLO On
16.0V
8.5V
16.0V
8.5V
UVLO Off
10.0V
7.9V
10.0V
7.9V
Maximum Duty
Cycle
<100%
<100%
<50%
<50%
BLOCK DIAGRAM
Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.
Note 2: Toggle flip flop used only in 1844A and 1845A.
SLUS224A - SEPTEMBER 1994 - REVISED APRIL 2002




Unitrode

UC2845A Datasheet Preview

UC2845A Datasheet

Current Mode PWM Controller

No Preview Available !

CONNECTION DIAGRAMS
ABSOLUTE MAXIMUM RATINGS (Note 1)
Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . 30V
Supply Voltage (ICC mA) . . . . . . . . . . . . . . . . . . . . Self Limiting
Output Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1A
Output Energy (Capacitive Load). . . . . . . . . . . . . . . . . . . . . 5µJ
Analog Inputs (Pins 2, 3). . . . . . . . . . . . . . . . . . . -0.3V to +6.3V
Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . 10mA
Power Dissipation at TA 25°C (DIL-8) . . . . . . . . . . . . . . . . 1W
Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C
Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . 300°C
Note 1. All voltages are with respect to Ground, Pin 5. Currents
are positive into, negative out of the specified terminal. Consult
Packaging Section of Databook for thermal limitations and con-
siderations of packages. Pin numbers refer to DIL package only.
SOIC-14 (TOP VIEW)
D Package
PLCC-20, LCC-20
(TOP VIEW)
Q, L Packages
UC1842A/3A/4A/5A
UC2842A/3A/4A/5A
UC3842A/3A/4A/5A
PACKAGE PIN FUNCTION
FUNCTION
PIN
N/C 1
Comp
2
N/C 3-4
VFB 5
N/C 6
ISENSE
7
N/C 8-9
RT/CT
10
N/C 11
Pwr Gnd
12
Gnd 13
N/C 14
Output
15
N/C 16
VC 17
VCC 18
N/C 19
VREF
20
SOIC-WIDE16 (TOP VIEW)
DW Package
N/C 1
N/C 2
COMP 3
VFB 4
ISENSE 5
RT/CT 6
N/C 7
N/C 8
DIL-8, SOIC-8 (TOP VIEW)
J or N, D8 Package
16 N/C
15 VREF
14 VCC
13 VCC
12 OUTPUT
11 GND
10 PWRGND
9 N/C
2


Part Number UC2845A
Description Current Mode PWM Controller
Maker Unitrode
Total Page 21 Pages
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